In an automobile, in order to widely use a compartment space of the vehicle, the seat is structured to be detachable from the vehicle floor or the seat back portion is structured to be reclined relative to the seat cushion. The reclining seat device or the detachable seat device is normally fixed to a vehicle fixed portion, such as a vehicle sidewall portion or the vehicle floor so as not to generate any noise that may influence on a vehicle comfort. In addition, a stout lock device is provided for preventing any unexpected release of the lock by an impact caused by a vehicle collision.
For example, a conventional door lock device 24 (numerals here are recited from a patent document 1 (specification and drawings of U.S. Pat. No. 6,945,585) is disclosed as shown in FIG. 3 or 4 of the document. The door lock device 24 of the document is fixed underneath a seat 10 and is engaged with a striker 29 fixed to a vehicle floor 20. In more detail, a side plate member 32 having an entrance/retracting groove is fixed underneath a seat member 22. The striker 29 is engaged with the entrance/retracting groove for locking. A latch 40 and a pawl 70 are rotationally supported on the side plate 32 and a spring force generated by a tension spring 78 gives each member a rotational force in opposite direction with each other. The striker 29 having entered into the groove of the side plate member 32 pushes a rear side groove surface of a lock groove 46 to rotate the latch 40 in a locking direction overcoming the spring force of the tension spring 78. Then a lock surface of the pawl 70 engages with the lock portion of the latch 40 to prevent the latch from rotating in a lock release direction. Under the locked position, the seat 10 is fixed to the vehicle floor 20 by firmly enclosing the striker 29 between the front side groove surface of the lock groove 46 and the bottom surface of the entrance/retracting groove of the side plate member 32.
In order to fittingly engage the striker with the latch 40 under the locked position, a cam member 48 is lineally movably installed and is biased by a return spring 54 in an opening direction of the lock groove 46. An inclined cam surface 52 is provided on the cam member 48 along the front side groove surface and accordingly when the cam member 48 advances by the force of return spring 54, the inclined cam surface 52 moves into the lock groove 46 to be firmly in contact with the striker 29 so that any chattering noise can be eliminated.
According to the lock device mentioned above (the patent document 1), it is necessary for the cam member 48 to be retracted in accordance with the rotation of the latch 40. This is because the cam member 48 is installed on the latch 40. If the inclination angle of the cam surface is small, the retracting movement of the cam member may be interrupted. Accordingly, it is necessary to provide a wide range inclination angle on the cam surface 52, which leads to a large pressing angle of the cam surface 52 on the striker 29 and when a force is applied on the cam surface 52 from the striker 29, the cam member 48 may retreat to loosen the engagement with the striker. The loosened engagement may lead to a generation of chattering noise.
Further, in the lock device according to the patent document 1, after the pawl 70 is disengaged from the latch 40, when the striker 29 is released from the lock device 24, the latch 40 is rotated keeping the firm engagement of the striker 29 with the cam surface 52 and the bottom surface of the entrance/retracting groove. This will need a greater force for disengaging the striker 29 from the lock device 24.
A need thus exists for a lock device, which is not susceptible to the drawback mentioned above.